The present invention relates generally to complexes of initiators and amidines. The complexes are useful in initiator systems for polymerization of monomers.
Systems for initiating the polymerization of monomers to make compositions, such as adhesives, are known in the art. U.S. Pat. Nos. 5,106,928, 5,286,821, and 5,310,835 to Skoultchi et al., for example, describe two-part initiator systems for initiating the polymerization of acrylic monomers. The first part of these two-part systems typically includes a stable organoborane amine complex and the second part includes an activator. The activator liberates the organoborane compound by removing the amine group, thereby allowing the organoborane compound to initiate the polymerization process. Activators are also sometimes referred to as liberators or decomplexers.
Common complexes in such systems include complexes of an organoborane and an amine. While such complexes may be useful in many applications, certain problems may arise due to the use of amine complexing agents in such conventional complexes. For example, when the complexes contain a primary amine, adhesives prepared therefrom may be prone to discoloration, such as yellowing. Furthermore, when including reactive diluents, such as aziridine-functional materials described in PCT Publication No. WO 98/17,694, for example, in compositions containing the complexes, the diluents may prematurely react with protic amines (i.e., those amines in which a nitrogen atom is bonded to at least one hydrogen atom) in such complexes, prematurely decomplexing the organoborane initiator. This phenomenon may even be to such an extent as to prematurely initiate polymerization of monomers present with the complexes or to degrade efficacy of the initiators for polymerization of subsequently added monomers.
In light of these potential problems and the desire to provide alternative formulations, further complexes are desirable, particularly for use in initiator systems, such as those used for polymerization of adhesives useful for bonding low surface energy substrates.
Initiator systems of the invention comprise a complexed initiator comprising a complex of an amidine complexing agent and an initiator; and a decomplexer. Preferably, the initiator comprises an organometallic initiator, such as an organoborane initiator.
Complexes of organoborane initiators and complexing agents of the invention may be represented by the following general Formula (I): 
wherein R1 is an alkyl group having 1 to about 10 carbon atoms. R2 and R3 may be the same or different and are selected from (i.e., they are independently selected from) alkyl groups having 1 to about 10 carbon atoms and phenyl-containing groups. xe2x80x9cCxxe2x80x9d represents a complexing agent of the invention. The value of xe2x80x9cvxe2x80x9d is selected so as to provide an effective ratio of amidine nitrogen atoms to boron atoms in the complex.
The initiator systems are useful for initiating polymerization of at least one monomer. To initiate polymerization in such a manner, at least one monomer is provided and then blended with the initiator system. Polymerization of the at least one monomer can be initiated as such.
The amidine complexing agents of the invention may be vinyligous or non-vinyligous. Furthermore, the amidine complexing agents may be protic or non-protic In one preferred embodiment, the amidine complexing agent comprises an amidine represented by Formula (II): 
wherein:
R4 is hydrogen or an organic group, preferably hydrogen or an alkyl or alkylene group;
R5 and R6 are independently a monovalent organic group or part of a cyclic structure; and
w, x, and y comprise integers, preferably w being 1 and x being about 3 or less.
Particularly preferred amidine complexing agents comprise those selected from the group consisting of N,N,Nxe2x80x2,Nxe2x80x2-tetramethylguanidine;
1,8-diazabicyclo[5.4.0]undec-7-ene;
1,5-diazabicyclo[4.3.0]non-5-ene; 2-methylimidazole; 2-methylimidazoline; and 4-(N,N-dimethylamino) -pyridine.
According to another aspect of the invention, the amidine complexing agents are used as part of a kit. In one embodiment, kits of the invention comprise
a polymerizable composition, wherein the polymerizable composition comprises:
at least one polymerizable monomer, and
at least one decomplexer; and
an initiator component, wherein the initiator component comprises:
a complexed amidine initiator, and
an optional diluent.
A bonding composition can be prepared by mixing the polymerizable composition of the kit with the respective initiator component. The bonding composition can be used, for example, to prepare substrates at least partially coated with the bonding composition and bonded articles comprising a first substrate and a second substrate, with the polymerized bonding composition adhesively bonding the first and second substrates together. The bonding compositions are particularly useful for coating low surface energy substrates.